Seljuk Turks can be regarded as the ancestors of Western Turks (today's Turkey, Turkmenistan, Uzbekistan and Azerbaijan). They and their descendants (i.e., the Ottoman Empire) played a major role in medieval times by setting a barrier against the Mongol onslaught, defending the Islamic world against Crusaders and bringing an end to the Byzantine Empire. The fact that they embraced Sunni Islam and defended it with an irresistible power is one of the reasons why this branch is the major and most populous division of Islam.